3D X-Ray Microtomography Reconstructions

The fossils from the Mazon Creek area of northeastern Illinois (Will, Grundy, Kankakee, LaSalle, and Livingston counties) comprise one of the most diverse floras for its age and one of the world's most important soft-bodied fossil faunas. This biota has been studied since the mid-19th century and extensively collected by both amateurs and professionals. The Field Museum's collections, comprising over 60,000 specimens, afford the most comprehensive representation of these fossils and have been extensively researched. New techniques and methodologies often allow exciting new insights to be gathered from these fossils and this is the case with the recent publication by Spencer, Hilton and Sutton in the journal Review of Palaeobotany and Palynology in which they apply 3D x-ray microtomography in combination with precision cutting techniques to the analysis of a pteridosperm ovule.

At coal measure localities such as Mazon Creek exceptional preservation of organic material can be found within early-diagenetic siderite (iron carbonate) nodules. The rapid envelopment of fossils within this concretionary material provides a high level of compressional resistance reducing and in many cases eliminating compaction. Therefore, recovery of well-preserved three-dimensional botanical material with cellular preservation is likely. Traditional methods of study involve serial sections using a combination of thin-sections and/or cellulose acetate peals (e.g. Drinnan et al., 1990). However, in employing this process, data loss through sawing is inevitable.

In recent years, advances in computational power and a reduction in the cost of X-ray microtomography (XMT) has seen this technology increasingly used for paleontological research; yet the number of palaeobotanical research projects that have used any sort of scanning technology remains low. XMT is a non-destructive technique that enables the capture and visualisation of 3D high resolution internal data from fossils, in a way previously unattainable.

Alan Spencer and Mark Sutton of Imperial College London and Jason Hilton from the University of Birmingham in the UK have recently used this technique in combination with wafering to describe a new species of Medullosan pteridosperm ovule from the Mazon Creek biota: Stephanospermum braidwoodensis. Their 3D reconstruction of the ovule correlated the geometries of different layers with tissue characteristics gathered from wafered sections, with the methodological combination presenting a virtual reconstruction of the specimen and also enabling positioning of serial sections of the holotype in predetermined positions. Besides hugely reducing the amount of material lost during the cutting porcess their study suggest that there are still more new species to be discovered from the Mazon Creek assemblage by the use of these exciting new methodologies.